1. Field of the Invention
The subject invention relates to motion and position monitoring systems and, more specifically, to methods and apparatus for ascertaining movement of a device to a predetermined position, for ascertaining the existence of a predetermined relative position between a ratchet member and a pawl, and to methods and apparatus for operating a movable character printing device or for monitoring movable characters or charactering bearing segments in printing equipment.
2. Prior-Art Statement
An advanced prior-art character printing apparatus is disclosed in U.S. Pat. No. 4,015,521, by Joseph J. Neff, issued Apr. 5, 1977 to the subject assignee. In that apparatus, a plurality of mutually parallel character segments are individually adjusted to various angular positions for a printout of different number or character combinations. This type of apparatus is enjoying a widespread increasing use in several applications where accuracy of the printout is indispensable. For instance, one growing application involves the processing and recordation of incoming, previously invoiced payments in utility companies, periodical publishing houses and similar institutions. Large banks have also commenced to use this type of printing equipment in their internal negotiable instrument and payment processing operations.
In brief, myriads of bank checks, payment stubs and other papers are processed each hour by the type of equipment shown in the above mentioned patent, so that even a printing error rate of as low as one in ten thousand could have very grave effects. Unfortunately, existing double-checking systems for detecting printing errors tend to be more onerous and distractive than the basic paper processing and printing operation itself. Equally unfortunately, numerous factors, such as power supply or solenoid failure, wear, breakage, jamming or stickiness of mechanical parts, contribute to the potential failure of printing segments to advance to their proper intended positions at every instant.
There thus exists a serious need for methods and apparatus for ascertaining movement of a device from a first position to a second position. Unfortunately, the prior art has inadequately met this need as to a variety of applications. For instance, U.S. Pat. Nos. 3,131,627, 3,596,593, 3,640,216, 3,654,860, 3,742,844 and 4,078,485 basically pursue prior-art approaches by providing and employing various extra clock wheel and pickup coil systems, cam, cam follower and transducer pickup combinations, code disc and commutator time pulse generating apparatus and similar additional equipment. The contents of U.S. Pat. Nos. 3,422,754, 3,730,085, 3,822,640, 4,033,256 and the patents of record in the above mentioned Neff U.S. Pat. No. 4,015,521 may also be of interest in this respect.